Maternal diabetes frequently interferes with fetal development but the mechanism of interference and its biochemical consequences are poorly understood. The extreme lability of the product of such pregnancies and the increased morbidity in survivors has been well documented. Presently available data suggest that marked abnormalities in body composition occurs. We propose to better document body composition variables (antipyrine space, corrected bromide space, intracellular water, subcutaneous fat, fingernail nitrogen content) in neonates of known diabetic mothers, normal neonates, macrosomic neonates of diabetic mothers and macrosomic neonates of non-diabetic mothers. We hope thereby to formulate a biochemical explanation for the abnormalities of infants of diabetic mothers and suggest improvement in management of diabetic pregnancies and their offspring in order to reduce mortality and morbidity.